ABSTRACT Across the U.S., a growing number of drinking water supplies have been found to be contaminated with per- and polyfluoroalkyl substances (PFAS). We first found that at least six million Americans in 22 states receive drinking water from sources that exceeded EPA?s 2016 guideline for PFOS and PFOA, and over 100 million Americans are estimated to have PFAS in their tap water. Over 400 DoD sites have known or suspected releases of PFAS. Our team found that proximity to military fire training areas and airports strongly predicts drinking water contamination due to the use of PFAS-containing aqueous film-forming foam (AFFF) for liquid fuel fires. Health concerns related to PFOA and PFOS include cancer, liver toxicity, high cholesterol, and reproductive and developmental effects. Following our first report on immunotoxicity, a 2016 National Toxicology Program systematic review concluded that both PFOS and PFOA are presumed immune hazards to humans. While elevated total cholesterol has been associated with PFAS exposure, our preliminary evidence suggests associations with specific lipoprotein subfractions that predict risk of cardiovascular disease. Despite the growing number of communities with documented PFAS exposures, there have been few epidemiological studies in communities with PFAS-impacted drinking water. As part of ATSDR?s multi-site study of health effects associated with exposures to PFAS-contaminated drinking water, we propose a study of PFAS health effects in two communities in Eastern Massachusetts where public drinking water supplies have been contaminated by PFAS from AFFF use at nearby fire training areas. Our proposal includes a combination of required elements according to ATSDR?s protocol and novel components, such as applying total extractable organofluorine (EOF) and non-targeted screening methods to provide a more complete assessment of PFAS exposures and analyzing lipoprotein fractions, body fat measurements, and metabolomics markers of lipid metabolism. Research partners include Silent Spring Institute, Harvard T.H. Chan School of Public Health, and Eastern Research Group, and community partner organizations include Massachusetts Breast Cancer Coalition (MBCC) in Hyannis and People of Ayer Concerned about the Environment (PACE). The primary aims are: Aim 1. Evaluate serum-PFAS levels, serum biomarkers of effects, and neurobehavioral outcomes in 1,000 adults and 350 children in two communities with AFFF contamination of public water supplies. Aim 2. Measure total extractable organofluorine and non-targeted PFAS profiles in blood samples from children and adults to provide a more complete assessment of total PFAS exposures. Aim 3. Evaluate associations between measured and estimated PFAS exposures and markers of elevated disease risks, such as lipoprotein subfractions, metabolomics markers of lipid metabolism, body fat measurements, and antibody concentrations.